Fecal immunochemical test (FIT) is a laboratory screening test to find out hidden blood in the stool. It detects the tiniest amount of blood and probably helps to identify colon cancer or polyps at the early stage and helps to reduce the risk of cancer.
Immunochemical analysis of feces detects blood in latent form or one that we cannot see with the naked eye. The presence of occult blood in the feces indicates slow and abundant bleeding in the gastrointestinal tract, which appears periodically.
Most often, internal bleeding occurs without unpleasant symptoms, which becomes difficult to identify. Each part of the digestive system can be an area of hidden bleeding. In this case, the doctor may use FIT to diagnose the possibility of cancer or polyps.
Why is the fecal immunochemical test done?
After a patient complaint, the doctor recommends a fecal immunochemical test when there is suspicion of internal bleeding. One gram of feces from a healthy person contains no more than 2 mg of hemoglobin in one day feces, and at least 2 ml of blood comes out with feces if there is internal bleeding. Additionally, the color and appearance of feces change accordingly.
If there is high bleeding in the duodenum or small intestine, the stool becomes dark, tarry in color, and can we see it. If there is bloody discharge in stool but not visible, then this condition is referred to as latent. In this case, it is considered for lab tests through the immunochemical method by analyzing feces for occult blood.
The reasons for gastrointestinal bleeding can be the cause of diseases such as:
- Peptic ulcer
- Ulcerative colitis
- Crohn’s disease
- Anal fissure
- Hemorrhoids (Piles )
- The presence of malignant and benign formations in the digestive tract
Additionally, the doctor will recommend you to undergo a fecal immunochemical test if you regularly show the following symptoms:
- Dyspepsia (frequent nausea, heartburn, flatulence, stool instability);
- Regular pain in the abdomen without any cause
- Anemia (After blood test)
- Rapid weight loss
- Loss of appetite
- Discomfort and painful defecation
- Chronic fatigue syndrome (due to decreased appetite and weight)
- Age after 40 years; a family history of cancer or bowel disease
What is the procedure for a fecal immunochemical test?
The immunochemical type of the fecal occult blood test is strictly specific for human hemoglobin, and it is much more convenient since it does not require any strict diet.
Sometimes certain foods and medications influence the result of the FIT. Like if there is blood present in the stool, it may show negative and vice-versa. To avoid such an outcome and further problems, a doctor may suggest you adhere to a special diet. For example:-
- Avoiding red meat, chicken, and fish; vegetables like courgette, horseradish, cucumbers, cabbage, broccoli, and tomatoes before 72 hours before the laboratory examination.
- Before the test, you can include dairy products (kefir, cottage cheese, milk, cheese, feta cheese, and fermented baked milk) in your diet.
- Additionally, vegetables (carrots, cabbage, potatoes) and fruits, rice, oat, and wheat are allowed.
- Avoid collecting samples if there is bleeding due to nipple fissure because of breastfeeding.
How to collect a stool sample for analysis?
- Collecting stool sample consists of understanding the basic rules and guidelines.
- Three days before the procedure, you should stop taking medicines with iron a, and the day before vitamin C (ascorbic acid) and Aspirin (acetylsalicylic acid).
- Seventy-two hours before the examination, it is necessary to stop any treatment and diagnostic procedures that at least somehow affect the organs of the gastrointestinal tract. Like, colonoscopy and sigmoidoscopy.
- The day before collecting a feces sample, the patient should not brush his teeth since a brush, especially a hard one, can accidentally injure the gums and provoke bleeding, which will give false results.
- Take a stool for the examination only after natural defecation. Do not use laxatives before the collection or give an enema, as this will misinterpret the result. Also, do not strain during a bowel movement.
- It is also necessary to make sure that no urine or vaginal discharge accidentally gets into the collected material. To do this, urinate before defecation, and then wash and dry the perineum with a simple towel.
- After defecation, collect the sample (from 3-4 areas of stool) and transfer it to a disposable container (lid must) with the help of a spatula. Purchase it at the nearest pharmacy if you don’t have any two of these to collect the sample.
- Only 1/3 of the container volume is enough for examination.
Additional tips for collecting samples:-
- Collect samples in the morning
- Collect the feces carefully so that they do not accidentally fall into the water. It is best to collect it in a clean and dry container or cover the toilet with plastic wrap so that the stool is directly on it.
- Avoid collecting material within 3-5 days after the end of menstruation, with hemorrhoidal bleeding. Aspirin, alcoholic beverages, and some anti-inflammatory drugs can cause severe irritation to the intestines (including the colon) and cause occult bleeding.
- If the diagnosis requires three stool samples at once, then collect it from three bowel movements in one day.
- It’s critical to deliver the collected sample to the clinic within the next three hours.
The fecal immunochemical test is one of the primary screening tests for colorectal cancer since tumor formation develops without severe symptoms and can detect minimal and regular bleeding.
FIT is the easiest, fastest, and “In vitro” study of internal bleeding, but for detailed information, you may need to undergo gastroscopy or colonoscopy.
Sending samples for analysis
You must deliver feces to the laboratory within three hours; if you can’t store it in the refrigerator. Though frozen or preserved samples are not suitable for diagnosis. To get an accurate result of the test, follow all these guidelines strictly.
What does the FIT result mean?
- A false-negative result of the fecal immunochemical test: The reason for a false-negative result can be not collecting samples with proper guidelines or less sample collected in a container. Also, in some diseases of the gastrointestinal tract, for example, polyps of the large intestine cause bleeding occasionally. Therefore, you need to repeat the test several times to avoid a false result.
- A false-positive result of an occult blood test is, in most cases, a result of not following guidelines. Either the patient did not follow the diet prescribed by the doctor, or took any medications that distorted the study, or injury, that led to blood entering the gastrointestinal tract.
Other reasons for false result can be:
- Feces collected during menstruation
- Anal fissures or hemorrhoids
- Bleeding from the nose
- Severe bleeding of the gums
The positive FIT result – what to do?
- If the result comes negative, it means there is no blood in your stool samples. If you belong to the risk group of colon cancer, the doctor will suggest you perform a FIT test yearly.
- If the test comes positive, there is blood in your stool; the doctor will recommend you to do an additional test to confirm the diagnosis.
What diseases does blood in the stool can indicate after the test?
If you carefully perform the entire procedure and after the test, if there is blood in the stool, even if the positive result turned out to be reliable, it may indicate the following large intestine diseases:
- Colorectal cancer
- Colonic polyps
- Ulcerative colitis
- Irritable bowel syndrome
- Hemorrhoids and anal fissure
Of course, all these diseases are potentially dangerous, but the main concern for people who have received a positive result is the risk of developing cancer. To fully understand the symptoms, it is necessary to go for an additional diagnostic technique such as abdominal ultrasonography, colonoscopy, and sigmoidoscopy.